1. Field of the Invention
The present invention relates to a semiconductor device, an electronic device, and a method for manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, flat panel displays such as liquid crystal display devices and electroluminescence (EL) display devices have attracted attention.
Driving methods of the flat panel displays include a passive matrix method and an active matrix method. An active matrix method has advantages over a passive matrix method in low power consumption, high definition, a large-sized substrate, and the like.
Here, a structural example of an active matrix liquid crystal panel is briefly described with reference to FIGS. 15A and 15B. FIG. 15A illustrates an example of a structure in which a driver circuit is provided using a tape automated bonding (TAB) method.
In FIG. 15A, a pixel portion 1501 in which pixels 1502 are arranged in matrix is formed over a substrate 1500 having an insulating surface. The pixels 1502 are arranged in matrix at intersections of scan lines extending from a scan line side input terminal 1503 and signal lines extending from a signal line side input terminal 1504. Each of the pixels in the pixel portion 1501 is provided with a switching element and a pixel electrode layer connected to the switching element. A typical example of the switching element is a TFT. A gate electrode layer side of the TFT is connected to a scan line, and a source or drain side of the TFT is connected to a signal line. In addition, an IC 1551 included in a driver circuit is connected to a flexible printed circuit (FPC) 1550.
In a structure where a driver circuit is provided outside a panel as in FIG. 15A, it is possible to use, as a driver circuit, an IC using a single-crystal silicon; therefore, a problem due to a speed of a driver circuit does not arise. However, when an IC is provided in this manner, the manufacturing cost cannot be reduced sufficiently because of necessity of preparing a panel and an IC separately, necessity of a step of connecting the panel and the IC, and the like. Further, the thickness of the liquid crystal panel is increased when the IC is connected, which leads to increase in the size of a frame region.
In terms of reduction in cost or a panel size, or the like, a method in which a pixel portion and a driver circuit are formed over the same substrate has been employed (e.g., see Patent Document 1: Japanese Published Patent Application No. H8-6053). FIG. 15B illustrates an example of a structure in which a pixel portion and a driver circuit portion are formed over the same substrate.
In the case illustrated in FIG. 15B, non-single-crystal silicon such as amorphous silicon, microcrystalline silicon, or polycrystalline silicon is used as a semiconductor layer of a driver circuit 1560, similar to the pixel portion. However, even in a case where microcrystalline silicon or polycrystalline silicon as well as amorphous silicon is used, there is a problem in that characteristics thereof are incomparable to characteristics of single-crystal silicon. In particular, in a semiconductor layer which is used for a conventional panel where a driver circuit is integrated, characteristics which are necessary and sufficient cannot be obtained. This has caused a big problem in manufacturing a driver circuit, that is, a semiconductor device where high speed operation is required.
In order to solve the above-described problem, a panel using silicon on insulator (SOI) technology is made on an experimental basis in recent years. In particular, when Smart Cut (registered trademark) is used, a single-crystal silicon thin film having high carrier mobility can be obtained by a very simple method (for example, see Patent Document 2: Japanese Published Patent Application No. H11-163363).